I’m currently using up 3 "comp" days…basically taking 3 days off in exchange for working that snowy Sunday back in late January plus this past weekend. My daughter had a planned preemptive surgery at Emanuel hospital today, so yesterday and today I didn’t look very closely at maps. But after running into several people at the hospital that thought it was going to snow in Portland soon, I figured I better take a look. The last I had checked it appeared that we’d see -7 850mb temps and snow sticking maybe down to around 1,500′ sometime Wednesday-Friday.
So what do I see? Lots of interesting weather possibilities, which may or may not have an impact on normal folks here in Portland.
First, the snow: The forecast 850mb temps haven’t changed from what was shown Sunday for late this week. At the end of March, to get STICKING snow down to the lowest elevations, you’d need all parameters to come together perfectly. Steady, heavy precipitation sometime between the hours of 10pm and 8am (nighttime), no mixing south wind, and that cold atmosphere we know is coming. First off, let’s remember the NAM has not done well this winter and in general doesn’t do as well as the GFS (for sure on low pressure placement!). It shows a comma-type trough feature moving into the southern/central Valley late tomorrow afternoon, turning winds light through the Valley too. This is very similar to the sudden 1-3" that fell one night this past winter from Woodburn to Eugene. The 00z GFS has the trough a bit farther north, keeping the mixing wind going, plus the timing isn’t during the night, so we’ll get 40-45 degree rain in the city tomorrow afternoon. I doubt we’ll get anything more than a dusting from 1,000-1,500′ between the Coast Range and Cascades the next 24 hours. Maybe nothing at all below 1,500′. I bet the west slopes of the Coast Range will see sticking snow down to 1,000′ since the precipitation will be more intense out there. Thursday should be much more showery with sunbreaks. This time of year we’ll be in the 45-50 degree range, so the snow level jumps up to at least 2,000-2,500′ in the afternoon, very similar to last Saturday. Friday is very interesting with a surface low forecast to track towards the N. Oregon Coast, then move inland into S.W. Washington. If the low is approaching the Coast in the early morning hours (before 8am), the brief offshore flow and steady, heavy precipitation COULD bring snow below 1,500′. That’s a big IF. So in general…those of you in the hills around 1,500′ will probably get a few shots of snow the next few days, with a dusting possible to 1,000′ in the late night hours. Better chance for a dusting below 1,000′ in the Coast Range and Cascade Foothills. Forget about it in the city…it would have to be a one-time freak occurrence. It would be as crazy as…having a tornado in January in Vancouver…
A new wrinkle this evening is about possible strong wind: As I mentioned, the 00z GFS MM-5 brings a surface low (while deepening) up into S.W. Washington Friday morning. The 10-12 mb OLM-EUG gradient could produce south wind gusts of 30-40 mph. The 00z NAM goes nutso…deeping the low to 985 mb up around Centralia. This gives 20-24 mb. in the same area! That’s major windstorm territory for the KLS-EUG corridor. BUT…it’s the NAM, so I would discount it for now, but there’s always 12z right? I’ve included both maps for comparison. Okay, checking out for now, maybe an update tomorrow evening again…Mark Nelsen